This invention relates to containers and is primarily concerned with those which have closure members which fit inside an opening and which can be turned to lock in place.
This requires an internal thread or some form of undercut, and with a moulded construction there are consequently manufacturing problems which are costly and difficult to overcome. Indeed they are sometimes considered impossible. Tool costs are high, and one either has to arrange for unscrewing a core from the newly formed thread or undercut or else collapsing the core sufficiently to permit its withdrawal. It has been attempted simply to pull the core out directly, forcing the plastics aside, but this often damages the plastics.
It is the aim of this invention to enable such a container to be manufactured more easily.
According to one aspect of the present invention there is provided a method of making a container to which entry is via an opening having a detent for positively retaining a closure member within that opening, the material of the container being susceptible to deformation when heated, wherein in a first stage an embryo container is formed with a surface which is to provide the inside of the opening exposed and facing outwardly, the detent being simultaneously formed on or in said surface, and wherein in a second stage the material defining the opening is deformed, at an elevated temperature, to transform said surface from an outwardly facing one into a passage providing the opening with the detent.
It will be assumed hereafter that both the embryo and finished container are in an upright attitude with the opening uppermost.
The formation of the embryo container in the first stage is conveniently by injection moulding using an inner mould core which is subsequently extractable through said opening, while the transformation from embryo to finished container in the second stage is preferably by blow moulding via the opening, although at least some of the distortion or stretching inherent in the process could be achieved mechanically.
The detent in the embryo container may be a spiral or part-spiral to form screw threading in the finished container. Alternatively, the detent could be at least one L-shaped indentation to form the female part of a bayonet fitting, or at least one stud to form the male part of a bayonet fitting. In another version, the detent is an annular ring formation to retain a ball, as used for roll-on deodorants for example.
In the preferred form, the material to define the opening is initially a generally radial flange at the mouth of a closed end tube, and said surface is the upper one of that flange. There may also be a generally cylindrical flange at the periphery of the radial flange projecting downwardly to surround the opening end of the tube. In the second stage, the radial flange is deformed downwards into a generally cylindrical configuration so that its under surface faces outwardly to co-operate with the inside of the cylindrical flange. In the finished container they bond together. The spiral (if that is the detent) becomes a screw thread on the inside of the opening.
With this arrangement, and if the material of the container is transparent, a data band can be provided on the inside of the cylindrical flange of the embryo container to be legible therethrough, the band being made captive by the deformed radial flange.
Conveniently, there is a rim projecting beyond the radial and cylindrical flanges, its underside providing means for locating the embryo container during the blow moulding while its inside provides a seat for a blow pin.
According to another aspect of the invention there is provided a container made by the method outlined above.